Flow line systems which transport potentially dangerous fluids, such as anhydrous ammonia, include a separable connection for emergency interruption of the flow line which extends between a stationary vessel and a potential portable vessel. Occasionally a transport vehicle pulls away from the stationary vessel prior to disconnecting the flexible flow line, and the absence of a separable connection may otherwise cause a rupture of the fill line. The monetary loss of fluid from such a rupture is nominal compared to the risks commonly associated with the release of toxic vapors. The involuntary release of anhydrous ammonia due to a rupture of a flow line during an advertent pullaway may seriously injure the operator, causing blindness, skin burns, or loss of smell. For other potentially dangerous fluids, such as propane and liquid petroleum gas, the release of the fluid during an inadvertent pullaway may cause adverse environmental consequences to the filling station site or create a fire hazard. One type of improved breakaway connection, marketed as the TRIPOD.TM. connection, is disclosed in U.S. Pat. Nos. 5,228,474 and 5,320,133. The TRIPOD.TM. connection is particularly suitable for positioning between a stationary filling platform and a transport vehicle.
In a typical anhydrous ammonia application system, a stationary nurse tank, which may be periodically filled by the above-described transport vehicle, is attached to anhydrous ammonia applicator with a mechanical hitch. Each end of the hose which connects the nurse tank and an applicator may include a shutoff valve. A breakaway coupling is provided between the shutoff valves, and is designed so that when properly mounted and maintained it will uncouple with a pull force so as not to damage the nurse tank. The primary purpose of the breakaway coupling is both to separate or breakaway and to shut off the flow of ammonia in the event of separation of the applicator and nurse tank at the mechanical hitch.
One type of breakaway coupling used in anhydrous ammonia application systems is the PIONEER.TM. coupling distributed by Parker Hannifin Corporation. When uncoupled or disconnected, poppet valves in each half of the coupling are closed by respective valve springs, thereby stopping the flow of ammonia to the atmosphere. When the coupling is either fully connected or fully disconnected, a spring positions a sleeve to prevent locking balls from rising up out of their ball holes. When fully connected, the poppet valves in both coupling halves are open to allow ammonia flow. When the axial pull on the male coupling half exceeds the force of the sleeve spring, the coupling male half will pull out of the socket. The poppet valve springs then close to stop the discharge of anhydrous ammonia from the flexible flow lines.
The PIONEER.TM. coupling has several problems which have been widely recognized in the marketplace for years. This coupling has a high failure rate in service and, in an attempt to reduce failures, the manufacturer provides that the coupling must be inspected thoroughly before each use of the applicator. Due in part to the complexity of the device and the number of components, the manufacturer recommends that this breakaway coupling when used in anhydrous ammonia applications be replaced once it is in service for three years. This relatively short life is very costly to the user, both in terms of the replacement cost for new couplings and the costs associated with the placement of the coupling. The device suffers from problems associated with the sticky poppets, and numerous components are susceptible to dirt and corrosion. As time goes by without a disconnect, the manufacturer notes the corrosion may make the poppet valve action sticky such that the valve spring will not be able to close the valves. The manufacturer recommends the device be carefully cleaned and lubricated, but in practice the user seldom follows the manufacturer's recommendations regarding service. Due to the design of the PIONEER.TM. coupling, the required axial force to cause a breakaway is a function of the fluid pressure passing through the coupling, which inherently contributes to unreliability. The PIONEER.TM. coupling is thus more difficult to trip and requires a larger axial force to separate when fluid pressure in the coupling is high, since increased fluid pressure acts between the balls and the sleeve to increase friction which must be overcome in order for the coupling to separate.
The disadvantages of the prior art are overcome by the present invention. An improved safety disconnect is disclosed herein for use in a fluid flow system, and particularly for use between an anhydrous ammonia nurse tank and an applicator. The coupling of the present invention may be used, however, in various other applications wherein flow lines extend between containers which may purposefully or inadvertently move relative to each other, such that the coupling will automatically separate during a pullaway and trap fluid with each separated coupling half.